Phase-shift modulation in double half-bridge inverter with common resonant capacitor for induction heating appliances

In this study, the application of the phase-shift modulation to a double half-bridge resonant inverter supplying inductive loads with a common resonant capacitor is analysed in order to control the output power provided to the load of each converter. This study is focused on the application of such modulation to a cost-effective solution for domestic induction heating appliances with at least two burners heating up simultaneously two pots. The burners, also called inductor-pot systems, are usually electrically modelled by their equivalent impedances, Z_coil(ω). The proposed modulation is suitable to control the power provided to inductor-pot systems with different equivalent impedances. The control variables of each half-bridge inverter, that is, switching frequency, f_swo, and duty cycle, D, have been assumed identical to both inverters in order to simplify the analysis, but, a new control parameter, the phase-shift between inverters, φ, is employed. In the analysis, it has been proved that the power dependence with respect to the phase-shift between the inverter is almost totally due to the first harmonic contribution of the current. Finally, the main results of the analysis are checked by means of experimental measurements.